Biometric systems are commonly used as an aid to confirming authorization for access to various types of resources or locations. Biometric systems measure various unique or nearly unique characteristics of a person's body to assist in confirming identity and, consequently, in authorizing an access requested by the person. The body characteristics, or biometric information, are measured by a biometric sensor, for example, a fingerprint sensor or an eye retinal scanner.
For the biometric system to authorize user access to a resource or location, the biometric information of the user has to be known by the biometric system and the biometric system has to verify the biometric information of the user when the user requests authorization. For the user to be known to the biometric system, the user will have to register or enrol its biometric information with the system. This process is often referred to as enrolment or registration. In the enrollment process, the biometric system receives biometric information from the biometric sensor and stores at least a portion of the biometric information to create a database of the biometric information. When verifying the user, the biometric system compares subsequently-received biometric information to the biometric information stored in the database, and if a sufficient match between the two is found the user is authorized to access the resource or location.
To enable biometric sensors to be incorporated onto smaller devices—e.g., smart phones—without taking up too much space on the device, and to minimize the costs of the sensor, sensors have become smaller and smaller. Thus, for example, a fingerprint sensor may image only a relatively small part of the user's finger, and the resulting fingerprint image is much smaller than the overall size of the finger surface. Some known methods reconstruct multiple smaller images into a large reference image. However, as images reconstruction is a lossy process due to e.g. elastic deformation of the fingerprint and limited sensor resolution, this introduces errors in the reference image. The enrollment and verification system will be able to verify the user only if data corresponding to the fingerprint image, i.e., the test image, is stored in the reference database in one or more of the reference images. If the test image corresponds to one part of the user's finger and the stored reference image(s) correspond to a different, non-overlapping part of the user's finger, the user cannot be verified.